Composite insulating bushing



Nav. 25, 1947. A. GAUDENZI El AL COMPQSITE INSULATING BUSHING Filed Sept. 15, 1945 2 Sheets-Sheet 1 Nov. 25, 1947 A. GAUDENZI Ei' AL COMPOSITE INSULATING BUSHING ZAEL -W Filed Sept. 13, 1945 2 Sheets-Sheet 2 INVENTORS B M flaws/1M.

Patented Nov. 25, 1947 UNITED STATES PATENT OFFICE COMPOSITE INSULATING BUSHING Arthur Gaudenzi, Wettingen, and Erwin Kerm.

Ennetbaden, Switzerland, assignors to Aktiengesellschaft Brown, Boveri & Cie, Baden, Switzerland, a joint-stock company Application September 13, 1945, Serial No. 616,002 In Switzerland October 5, 1944 14 Claims. (Cl. 174-152) operation are particularly desirable. It has been proposed to solve this problem by the use of fused joints between a metallic member and a ceramic member by means of fusible glass or enamel compositions. Such fused joints present definite surfaces of separation. .The tightness of such joints under the effect of large or steep temperature changes depends upon the degree of uniformity of temperature coefficients of expansion of the various materials. The same disadvantage occurs when a metallic layer is sprayed or otherwise attached to a ceramic member to which a metal member is then soldered or welded.

The difficulties. arising from the presence of definite surfaces of separation between members of different composition (conductors and nonconductors) can be avoided by utilizing the possibilities of modern sinter -technique to provide sintered articles suitable for direct welding to meta1 parts wherein a progressive transition from metal to non-metal, and the reverse, is provided.

The composite articles of the invention com-.

prise sintered articles consisting of a mixture of electrically conducting and non-conducting substances in comminuted form, pressed and sintered together, the relative proportions of the components being graded within the article to provide at least one electrically conducting surface porvessel of a mercury vapor rectifier, through which passes an electrode 2 bearing a flange 3. In Fig. 1 the members 4a, 4b electrically insulate theelectrode from the vessel while uniting the electrode vacuum-tight to the vessel. These members 40 and 4b are pressed and sintered bodies consisting of a mixture of a pulverized metal, for example iron. and a pulverized insulating material. The insulating material may be an oxide of an alkali metal (sodium, potassium), of an alkaline earth metal (calcium, barium, strontium) or of aluminum. Oxides of the elements of the carbon-- series (zirconium, titanium, thorium and silicon) may also beused as the non-conducting compotionwith the conductivity progressively decreasing from said portion to an insulating portion. In the accompanying drawing Figs. 1, 2 and 3 are diagrammatic sections showing typical embodiments of the invention in the production of vacuum-tight insulating bushings for conductors through the metal vessel of an electrical discharge apparatusiQthe sintered members of the invention providingsurfaces weldable on one side to the metal vessel and on the other side to the conductor with an insulating portion between the weldable surface portions.

In the drawings! is the wall of the metallic nent as well as minerals which consist essentially of an oxide or a silicate (kaolin, clay, quartz, steatite, talc, feldspar) and glass and porcelain compositions.

The composite articles may, as illustrated in Fig. 3, be advantageously made by placing in a press mold first pure metal powder, then a mixture of powdered metal and powdered insulating substance wherein the proportion of metal powder is decreased and the proportion of the insulating substance is increased as the height of the layer in the mold increases'to about the middle of the mold and thereafter gradually increasing the proportion of metal powder and decreasing the proportion of insulating substances and finally a layer of pure metal powder 'is provided at the top of the mold. After pressing and sintering the article possesses a gradually decreasing conductivity from the opposite end surfaces toward the middle. In the figures, the diminishing relative conductivity of the articles is indicated by an increase in the intensity of the shading from the surfaces at which the articles are welded to the flange 3' and the vessel l. The members may be brazed or soldered together as well as Welded.

In the production of the articles 4a, 4b the conductivity may be varied either uniformly or stepwise-by suitable layering or mixing of the two components of the mixture.

The vacuum-tightness of the articles may be increased by treating their surfaces or by impregnating them with oils, resins, enamel glazing compositions or synthetic resins, in which case only one of the members, for example, to, may be needed in the construction of Fig. 1. The space between members do and 4b in Fig. 1 may be filled with an insulating liquid of low vapor pressure to increase the vacuum-tightness of the construction.

Constructions of this type can be used not a plurality of serially alined ring members AL. 42, 43 welded to each/other and, at the ends of the series to the vessel I and flange 3, respectively as shown in Fig. 2.

In the production of insulating bushings for high potentials, portions or layers of progressively increased conductivity may be provided in suitable portions of the bushing, in order to obtain a distribution of stress in the bushing.

In the construction of Fi 2, the welded surfaces of adjacent ring members may be utilized for carrying connections to control grids or auxiliary electrodes.

In the construction illustrated in Fig. 3, the insulation bushing construction comprises a plurality of concentrically spaced pressed and sinteredannular layers or members whose conductivities decrease stepwise from the opposite end surfaces toward the middle. Each of layers 5| and 5|, which.are adjacent metal member l, consists of iron powder 100%; each of layers 52 and 52' consists of iron powder 80% and powdered insulating (ceramic) substance 20%; each of layers 53 and 53 consists of iron powder 50% and powdered insulating (ceramic) substance 50%; and each of layers 54 consists of iron powder 5% and powdered insulating (ceramic) substance 95%. Layers 55 and 55 have the same composition as have layers 53, 53; layers 56 and 56 have the same composition as have layers 52, 52; and layers 5'l and 51, which are adjacent metal member 3, have the same composition as have layers 5|, 5|. The space 58 therebetween is filled with a body 59 of insulating liquid of low vapor pressure. The outer (peripheral) surfaces of layers 5l-57, inclusive, are provided with a vacuum-tight coating layer 60 of resin or enamel glazing composition.

In the production of the articles it is advantageous to moisten the mixture with oil (vaseline, parafiin, or machine oil) to facilitate the pressing and the release of the form from the pressing mold and to prevent oxidation of the metal component of the mixture.

The metal component of the mixture may consist of pure metals or of mixtures or alloys of metals, both resistant and non-resistant to mercury according to the intended use.

We claim:

1. Article adapted to be welded to spaced metal parts, comprising a body of a pressed and sintered mixture of a pulverulent metal and a pulverulent insulating substance, the proportion of metal and insulating substance being progressively varied from portion to portion of the article to provide electrically-conductive surfaces at opposite ex-.- tremities of said body and an electrically insulating portion between the extremities.

2. Article as defined in claim 1 in which the proportions of metal and insulating material vary continuously through the article.

3. Article as defined in claim 1 in which the insulating substance is an oxide of a metal selected from the group consisting of alkali metals and alkaline earth metals.

4. Article as defined in claim 1 in which the insulating substance is an oxide of a metal of the carbon group.

5. Article as defined in claim 1 in which the insulating substance is aluminum oxide.

6. An article as defined-in claim 1 in which the insulating substance comprises a silicate.

7. A vacuum-tight insulating bushing construction for conveying a conductor through the metal vessel of an electrical discharge device comprising an annular member consisting of a pressed and sintered mixture of a pulverulent metal and a pulverulent insulating substance, the proportion of metal and insulating substance being progressively varied from portion to portion to provide adjacent one extremity of said annular member an electrically conductive surface portion welded vacuum-tight to the metal vessel, adjacent the opposite extremity a. second electrically conductive surface portion welded to the conductor, and. an electrically insulating portion therebetween.

8. An insulating bushing construction comprising a plurality of concentrically spaced annular members as defined in claim 7.

9. An insulating bushing construction comprising a plurality of concentrically spaced annular members as defined in claim '7 and an insulating liquid of low vapor pressure in the space therebetween.

10. An insulating bushing construction as defined in claim 7 wherein the surfaces of saidannular member are provided with a vacuum-tight coating.

11. An insulating bushing construction as defined in claim 7 wherein said annular member is impregnated with a vacuum-tight composition.

12. An insulating bushing construction comprising a series of annular members as defined in claim 7 welded together at adjoining surfaces.

13. An insulating bushing construction com-- prising a series of annular members as defined in claim 7 welded together at adjoining surfaces to provide bushings for the introduction of connections for auxiliary electrodes.

14. Article adapted to be Welded to spaced metal parts, comprising a body of a pressed and sintered mixture of a pulverulent metal and a pulverulent insulating substance, the roportions of metal and insulating material being varied stepwise in successive layers of the body to provide electrically conductive surfaces at opposite extremities of said body and an electrically insulating portion between the extremities.

' ARTHUR GAUDENZI.

ERWIN KERN.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,371,924 Moore Mar. 15, 1921 1,562,533 Weintraub Nov. 24, 1925 2,104,784 Weigand Jan. 11, 1938 2,147,417 Bahls Feb. 14, 1939 FOREIGN PATENTS Number Country Date 103,942 Switzerland 1924 

